1. Field of the Invention
The present invention relates to methods for remodeling soft tissue of a patient and, preferably, for remodeling the left ventricle of a patient's heart. The present invention also relates to systems for accomplishing the preferred methods.
2. Description of the Related Art
Congestive heart failure is a description given to a myriad of symptoms that may be the result of the heart's inability to meet the body's demand for blood flow. Heart failure may be considered as the condition in which an abnormality of cardiac function is responsible for the inability of the heart to pump blood at a rate commensurate with the requirements of the metabolizing tissues, or can do so only at an abnormally elevated filling pressure. There are many specific disease processes that can lead to heart failure. Typically, these processes result in dilation of the left ventricular chamber.
The process of ventricular dilation may be the result of chronic volume overload or may result from a specific damage to the myocardium. In a normal heart that is exposed to long-term increased cardiac output requirements, for example, that of an athlete, there is an adaptive process of slight ventricular dilation and muscle hypertrophy. In this way, the heart compensates for the increased cardiac output requirements. With damage to the myocardium, or chronic overload, however, there are increased requirements put on the contracting myocardium to such a level that this compensated state is never achieved and the heart continues to dilate.
One condition that is likely to reduce the blood pumping efficiency of the heart muscle is ventricular dilation. As the chamber becomes enlarged, the internal surface area of the chamber increases rapidly. Blood flowing within the heart applies pressure to the internal surface of the heart chamber and because the blood applies pressure inside the heart chamber across an increased surface area, the force which must be produced by the heart in order to pump blood also increases. In many cases, the cardiac disease responsible for the ventricular dilation also limits the ability of the heart muscle to produce the increased force required to efficiently pump blood, which further compounds the problem.
In many cases, the dilation of the heart chamber becomes progressively worse and the blood pumping efficiency of the heart muscle progressively declines. As this situation worsens, the location area of compromised myocardium may bulge out as the heart contracts, further decreasing the heart's ability to move blood forward. When local wall motion moves in this way it is said to be dyskinetic. The dyskinetic portion of the myocardium may stretch and eventually form an aneurismic bulge.
There is no cure for heart failure, but it can be treated. The primary goals of treatment are to relieve symptoms and prevent worsening of the condition. Symptoms may be relieved by removing excess fluid from the body, improving blood flow and increasing delivery of oxygen to the body tissues. Medical treatment usually comprises lifestyle changes and medications. For example, diuretics have been used to reduce extra cellular fluid which accumulates in congestive heart failure patients, thereby increasing the preloaded condition of the heart. Nitrates, arteriolar vasodilators and angiotensin converting enzyme (ACE) inhibitors have been used to treat heart failure through the reduction of cardiac workload by reducing afterload. Inotropes function to increase cardiac output by increasing the force and speed of cardiac muscle contraction. These drug therapies offer some beneficial effects, but do not stop the progression of the disease.
With respect to the situation of a dilated left ventricle or aneurism bulge, a variety of surgical studies have demonstrated some clinical success of ventricular remodeling and treatment of the dilation of the infarcted ventricle. One such remodeling procedure is referred to as the Batista Procedure. In the Batista Procedure, a small portion of the enlarged lower left ventricle chamber of the heart is removed to reduce the size of the left ventricle towards normal. Typically, the Bastista procedure involves the surgeon locating the left anterior descending coronary artery and making two small cuts down and outward to remove a wedge of the left ventricle. The remaining edges of the left ventricle are sewn together, returning the chamber to near its normal size. The incision is closed and the surgery is completed.
A variation of the Batista Procedure, referred to as the Dor Procedure, involves a lengthwise incision in the left ventricle along an area damaged by a myocardial infarction. The undamaged areas of the ventricle are sutured back together, eliminating the affected area. If the damaged area is too large, a patch may be used to cover the damaged area. However, in each of the Batista and Dor procedures, restoration of normal ventricular shape is a complex surgical procedure and very invasive for the patient. Furthermore, these procedures are not applicable to those patients that are not candidates for such invasive surgery.